arXiv subjects

Renata Kallosh

Publications and source records attributed to Renata Kallosh.

At least 91 records · Page 5Linked to original sources

arXiv2016

String Theory Origin of Constrained Multiplets

We study the non-linearly realized spontaneously broken supersymmetry of the (anti-)D3-brane action in type IIB string theory. The worldvolume fields are one vector $A_μ$, three complex scalars $ϕ^i$ and four 4d fermions $λ^0$, $λ^i$. These transform, in addition to the more familiar N=4 linear supersymmetry, also under 16 spontaneously broken, non-linearly realized supersymmetries. We argue that the worldvolume fields can be packaged into the following constrained 4d non-linear N=1 multiplets: four chiral multiplets $S$, $Y^i$ that satisfy $S^2=SY^i=0$ and contain the worldvolume fermions $λ^0$ and $λ^i$; and four chiral multiplets $W_α$, $H^i$ that satisfy $S W_α=0$ and $S \bar D_{\dot α} \bar H^{\bar \imath}=0$ and contain the vector $A_μ$ and the scalars $ϕ^i$. We also discuss how placing an anti-D3-brane on top of intersecting O7-planes can lead to an orthogonal multiplet $Φ$ that satisfies $S(Φ-\bar Φ)=0$, which is particularly interesting for inflationary cosmology.

hep-th↗

arXiv2016

Cosmological Attractors and Asymptotic Freedom of the Inflaton Field

We show that the inflaton coupling to all other fields is exponentially suppressed during inflation in the cosmological $α$-attractor models. In the context of supergravity, this feature is a consequence of the underlying hyperbolic geometry of the moduli space which has a flat direction corresponding to the inflaton field. A combination of these factors protects the asymptotic flatness of the inflaton potential.

hep-th↗

arXiv2016

Orthogonal Nilpotent Superfields from Linear Models

We derive supersymmetry/supergravity models with constrained orthogonal nilpotent superfields from the linear models in the formal limit where the masses of the sgoldstino, inflatino and sinflaton tend to infinity. The case where the sinflaton mass remains finite leads to a model with a `relaxed' constraint, where the sinflaton remains an independent field. Our procedure is equivalent to a requirement that some of the components of the curvature of the moduli space tend to infinity.

hep-th↗

arXiv2016

Linear Versus Non-linear Supersymmetry, in General

We study superconformal and supergravity models with constrained superfields. The underlying version of such models with all unconstrained superfields and linearly realized supersymmetry is presented here, in addition to the physical multiplets there are Lagrange multiplier (LM) superfields. Once the equations of motion for the LM superfields are solved, some of the physical superfields become constrained. The linear supersymmetry of the original models becomes non-linearly realized, its exact form can be deduced from the original linear supersymmetry. Known examples of constrained superfields are shown to require the following LM's: chiral superfields, linear superfields, general complex superfields, some of them are multiplets with a spin.

hep-th↗

arXiv2016

Coupling the Inflationary Sector to Matter

We describe the coupling of matter fields to an inflationary sector of supergravity, the inflaton $Φ$ and a stabilizer $S$, in models where the Kahler potential has a flat inflaton direction. Such models include, in particular, advanced versions of the hyperbolic $α$-attractor models with a flat inflaton direction Kahler potential, providing a good fit to the observational data. If the superpotential is at least quadratic in the matter fields $U^{i}$, with restricted couplings to the inflaton sector, we prove that under certain conditions: i) The presence of the matter fields does not affect a successful inflationary evolution. ii) There are no tachyons in the matter sector during and after inflation. iii) The matter masses squared are higher than $3H^2$ during inflation. The simplest class of theories satisfying all required conditions is provided by models with a flat direction Kahler potential, and with the inflaton $Φ$ and a stabilizer $S$ belonging to a hidden sector, so that matter fields have no direct coupling to the inflationary sector in the Kahler potential and in the superpotential.

hep-th↗

arXiv2016

Construction of the de Sitter supergravity

Recently, the complete action for an N=1 pure supergravity action in 4 dimensions that allows a positive, negative or zero cosmological constant has been constructed. The action is the generalization of a Volkov-Akulov action for the Goldstino coupled to supergravity. The construction uses a nilpotent multiplet. This paper is written in honour of Philippe Spindel. AVP enjoyed collaborations and many interactions with Philippe, who has always appreciated very precise derivations. We use this occasion to give a very detailed account of the calculations that lead to the published results. We review aspects of supersymmetry with de Sitter backgrounds, the treatment of auxiliary fields, and other ingredients in the construction.

hep-th↗

arXiv2016

Cosmology with orthogonal nilpotent superfields

We study the application of a supersymmetric model with two constrained supermultiplets to inflationary cosmology. The first superfield S is a stabilizer chiral superfield satisfying a nilpotency condition of degree 2, S^2=0. The second superfield Phi is the inflaton chiral superfield, which can be combined into a real superfield B=(Phi-Phi*)/2i. The real superfield B is orthogonal to S, S B=0, and satisfies a nilpotency condition of degree 3, B^3=0. We show that these constraints remove from the spectrum the complex scalar sgoldstino, the real scalar inflaton partner (i.e. the "sinflaton"), and the fermionic inflatino. The corresponding supergravity model with de Sitter vacua describes a graviton, a massive gravitino, and one real scalar inflaton, with both the goldstino and inflatino being absent in unitary gauge. We also discuss relaxed superfield constraints where S^2=0 and S Phi* is chiral, which removes the sgoldstino and inflatino, but leaves the sinflaton in the spectrum. The cosmological model building in both of these inflatino-less models offers some advantages over existing constructions.

hep-th↗

arXiv2015

Inflatino-less Cosmology

We construct inflationary models in the context of supergravity with orthogonal nilpotent superfields [1]. When local supersymmetry is gauge-fixed in the unitary gauge, these models describe theories with only a single real scalar (the inflaton), a graviton and a gravitino. Critically, there is no inflatino, no sgoldstino, and no sinflaton in these models. This dramatically simplifies cosmological models which can simultaneously describe inflation, dark energy and SUSY breaking.

hep-th↗

arXiv2015

From Linear to Non-linear Supersymmetry via Functional Integration

We derive a complete pure de Sitter supergravity action with non-linearly realized supersymmetry and its rigid limit, the Volkov-Akulov action, from the corresponding models with linear supersymmetry, by computing the path integral in the limit of infinite sgoldstino mass. In this, we use a non-Gaussian functional integration formula that was recently discovered in a derivation of de Sitter supergravity from the superconformal theory. We also present explicit examples of pure dS supergravity and the case with one matter multiplet. These two simple examples serve as a test and a demo of the universal action formula valid for de Sitter supergravities with general matter coupling.

hep-th↗

arXiv2015

De Sitter Supergravity Model Building

We present the explicit de Sitter supergravity action describing the interaction of supergravity with an arbitrary number of chiral and vector multiplets as well as one nilpotent chiral multiplet. The action has a non-Gaussian dependence on the auxiliary field of the nilpotent multiplet, however, it can be integrated out for an arbitrary matter-coupled supergravity. The general supergravity action with a given Kahler potential $K$, superpotential $W$ and vector matrix $f_{AB}$ interacting with a nilpotent chiral multiplet consists of the standard supergravity action defined by $K$, $W$ and $f_{AB}$ where the scalar in the nilpotent multiplet has to be replaced by a bilinear combination of the fermion in the nilpotent multiplet divided by the Gaussian value of the auxiliary field. All additional contributions to the action start with terms quartic and higher order in the fermion of the nilpotent multiplet. These are given by a simple universal closed form expression.

hep-th↗

arXiv2015

Matter-coupled de Sitter Supergravity

De Sitter supergravity describes interaction of supergravity with general chiral and vector multiplets as well as one nilpotent chiral multiplet. The extra universal positive term in the potential due to the nilpotent multiplet, corresponding to the anti-D3 brane in string theory, supports de Sitter vacua in these supergravity models. In the flat space limit these supergravity models include the Volkov-Akulov model with a non-linearly realized supersymmetry. The rules for constructing pure de Sitter supergravity action are generalized here in presence of other matter multiplets. We present a strategy to derive the complete closed form general supergravity action with a given Kahler potential $K$, superpotential $W$ and vector matrix $f_{AB}$ interacting with a nilpotent chiral multiplet. It has the potential $V=e^K(|F^2 |+ |DW|^2 - 3 |W|^2)$, where $F$ is a necessarily non-vanishing value of the auxiliary field of the nilpotent multiplet. De Sitter vacua are present under simple condition that $|F^2|- 3|W|^2>0$. A complete explicit action in the unitary gauge is presented.

hep-th↗

arXiv2015

String Theory Realizations of the Nilpotent Goldstino

We describe in detail how the spectrum of a single anti-D3-brane in four-dimensional orientifolded IIB string models reproduces precisely the field content of a nilpotent chiral superfield with the only physical component corresponding to the fermionic goldstino. In particular we explicitly consider a single anti-D3-brane on top of an O3-plane in warped throats, induced by $(2,1)$ fluxes. More general systems including several anti-branes and other orientifold planes are also discussed. This provides further evidence to the claim that non-linearly realized supersymmetry due to the presence of antibranes in string theory can be described by supersymmetric theories including nilpotent superfields. Implications to the KKLT and related scenarios of de Sitter moduli stabilization, to cosmology and to the structure of soft SUSY-breaking terms are briefly discussed.

hep-th↗

arXiv2015

Cosmological Attractors and Initial Conditions for Inflation

Inflationary $α$-attractor models in supergravity, which provide excellent fits to the latest observational data, are based on the Poincare disk hyperbolic geometry. We refine these models by constructing Kahler potentials with built-in inflaton shift symmetry and by making a canonical choice of the goldstino Kahler potential. The refined models are stable with respect to all scalar fields at all $α$, no additional stabilization terms are required. The scalar potential V has a nearly Minkowski minimum at small values of the inflaton field $φ$, and an infinitely long dS valley of constant depth and width at large $φ$. Because of the infinite length of this shift-symmetric valley, the initial value of the inflaton field at the Planck density is expected to be extremely large. We show that the inflaton field $φ$ does not change much until all fields lose their energy and fall to the bottom of the dS valley at large $φ$. This provides natural initial conditions for inflation driven by the inflaton field slowly rolling along the dS valley towards the minimum of the potential at small $φ$. A detailed description of this process is given for $α$-attractors in supergravity, but we believe that our general conclusions concerning naturalness of initial conditions for inflation are valid for a broad class of inflationary models with sufficiently flat potentials.

hep-th↗

arXiv2015

$α$-Attractors: Planck, LHC and Dark Energy

We develop four-parameter supergravity models of inflation and dark energy, constrained so that ${δρ\over ρ}$, $n_s$ and the cosmological constant $Λ$ take their known observable values, but where the mass of gravitino $m_{3/2}$ and the tensor-to-scalar ratio $r$ are free parameters. We focus on generalized cosmological $α$-attractor models, with logarithmic Kahler potentials, a nilpotent goldstino and spontaneously broken supersymmetry at the de Sitter minimum. The future data on B-modes will specify the parameter $α$, measuring the geometry of the Kahler, manifold. The string landscape idea for dark energy is supported in these models via an incomplete cancellation of the universal positive goldstino and negative gravitino contribution. The scale of SUSY breaking M related to the mass of gravitino in our models is a controllable parameter, independent on the scale of inflation, it will be constrained by LHC data and future collider Energy-frontier experiments.

hep-th↗

arXiv2015

$\overline{\rm D3}$ and dS

The role of the $\overline{\rm D3}$ brane in providing de Sitter vacua with spontaneously broken supersymmetry in the KKLT construction is clarified. The first step in this direction was explained in arXiv:hep-th/0301240, arXiv:hep-th/0308055: it was shown there that in the GKP background the bosonic contributions to the vacuum energy from the DBI and WZ term cancel for a D3 brane, but double for a $\overline{\rm D3}$ brane, leading to de Sitter vacua. The next step was taken in arXiv:1411.1121 where the analogous mechanism of the doubling (cancelation) of the $\overline{\rm D3}$ (D3) DBI and WZ terms was discovered in the presence of Volkov-Akulov fermions living on the brane, in a flat supergravity background. Here we confirm this mechanism of doubling/cancelation for the $\overline{\rm D3}$/D3 brane in the GKP supergravity background preserving $\mathcal{N}=1$, $d=4$ supersymmetry. We find that imaginary self-dual $G_{(3)}$ flux of type $(2,1)$ nicely removes the $SU(3)$ fermion triplet by giving it a large mass, while leaving the Volkov-Akulov goldstino, which is the $SU(3)$ singlet, massless. This makes the de Sitter landscape in D-brane physics clearly related to de Sitter vacua in effective $d=4$ supergravity with a nilpotent multiplet and spontaneously broken supersymmetry.

hep-th↗

arXiv2015

Escher in the Sky

The cosmological models called $α$-attractors provide an excellent fit to the latest observational data. Their predictions $n_{s} = 1-2/N$ and $r = 12α/N^{2}$ are very robust with respect to the modifications of the inflaton potential. An intriguing interpretation of $α$-attractors is based on a geometric moduli space with a boundary: a Poincare disk model of a hyperbolic geometry with the radius $\sqrt{3α}$, beautifully represented by the Escher's picture Circle Limit IV. In such models, the amplitude of the gravitational waves is proportional to the square of the radius of the Poincare disk.

hep-th↗

arXiv2015

The Hyperbolic Geometry of Cosmological Attractors

Cosmological alpha-attractors give a natural explanation for the spectral index n_s of inflation as measured by Planck while predicting a range for the tensor-to-scalar ratio r, consistent with all observations, to be measured more precisely in future detection of gravity waves. Their embedding into supergravity exploits the hyperbolic geometry of the Poincare disk or half-plane. These geometries are isometric under Mobius transformations, which include the shift symmetry of the inflaton field. We introduce a new Kahler potential frame that explicitly preserves this symmetry, enabling the inflaton to be light. Moreover, we include higher-order curvature deformations, which can stabilize a direction orthogonal to the inflationary trajectory. We illustrate this new framework by stabilizing the single superfield alpha-attractors.

hep-th↗

arXiv2015

Planck, LHC, and $α$-attractors

We describe a simple class of cosmological models called $α$ attractors, which provide an excellent fit to the latest Planck data. These theories are most naturally formulated in the context of supergravity with logarithmic Kahler potentials. We develop generalized versions of these models which can describe not only inflation but also dark energy and supersymmetry breaking.

astro-ph.CO↗